Magnetic recording medium

Abstract

Provided is a particulate magnetic recording medium having excellent electromagnetic characteristics, especially, a particulate magnetic recording medium which achieves a high output and a low noise and which is suitable for reproduction with an MR head. A magnetic recording medium comprising a flexible nonmagnetic support having thereon, in order, a nonmagnetic layer containing a nonmagnetic powder and a binder and at least two magnetic layers including an uppermost magnetic layer and a lowermost magnetic layer, each containing a ferromagnetic powder and a binder, wherein said at least two magnetic layers have a total thickness of from 0.02 μm to 0.5 μm and an average particle volume V(u) and a saturation magnetization σs(u) of a ferromagnetic powder in said uppermost magnetic layer are, respectively, higher than an average particle volume V(L) and a saturation magnetization σs(L) of a ferromagnetic powder in said lowermost magnetic layer.

What is claimed is:  
     
       1. A magnetic recording medium comprising a flexible nonmagnetic support having thereon, in order, a nonmagnetic layer containing a nonmagnetic powder and a binder and at least two magnetic layers including an uppermost magnetic layer and a lowermost magnetic layer, each containing a ferromagnetic powder and a binder, wherein said at least two magnetic layers have total thickness of from 0.02 μm to 0.5 μm and an average particle volume V(u) and a saturation magnetization σs(u) of a ferromagnetic powder in said uppermost magnetic layer are, respectively, higher than an average particle volume V(L) and a saturation magnetization σs(L) of a ferromagnetic powder in said lowermost magnetic layer, and wherein V(u) is in the range of from 5,000 to 50,000 nm 3  and V(L) is in the range of from 1,000 to 20,000 nm 3 . 
     
     
       2. The magnetic recording medium of  claim 1 , wherein a thickness d(u) of said uppermost magnetic layer and a thickness d(L) of said lowermost magnetic layer satisfy the following relation; d(u):d(L)=2:8 to 8:2. 
     
     
       3. The magnetic recording medium of  claim 2 , wherein said thickness d(u) and said thickness d(L) satisfy the following relation; d(u):d(L)=3:7 to 7:3. 
     
     
       4. The magnetic recording medium of  claim 1 , wherein said uppermost magnetic layer and said lowermost magnetic layer, each, has Hc equal to or higher than 2000 Oe. 
     
     
       5. The magnetic recording medium of  claim 1 , wherein said ferromagnetic powder contained in said uppermost magnetic layer is an acicular alloy magnetic powder containing Fe as a main component and said ferromagnetic powder contained in said lowermost magnetic layer is an acicular alloy magnetic powder containing Fe as a main component or a magnetoplumbite hexagonal ferrite. 
     
     
       6. The magnetic recording medium of  claim 1 , wherein said at least two magnetic layers have a total thickness of from 0.04 μm to 0.2 μm. 
     
     
       7. The magnetic recording medium of  claim 1 , wherein a ratio of said average particle volume V(u) and said average particle volume V(L) is in the range of from 1.5 to 10. 
     
     
       8. The magnetic recording medium of  claim 1 , wherein said saturation magnetization σs(u) is in the range of from 100 to 160 emu/g and said saturation magnetization σs(L) is in the range of from 50 to 150 emu/g. 
     
     
       9. The magnetic recording medium of  claim 8 , wherein a subtraction of said σs(L) from said σs(u) is in the range of from 20 to 80 emu/g. 
     
     
       10. The magnetic recording medium of  claim 1 , wherein said saturation magnetization σs(u) is in the range of from 110 to 155 emu/g and said saturation magnetization σs(L) is in the range of from 55 to 130 emu/g. 
     
     
       11. The magnetic recording medium of  claim 1 , wherein said uppermost magnetic layer and said lowermost magnetic layer, each, has a coercive force (Hc) from 2,000 to 4,000 Oe. 
     
     
       12. The magnetic recording medium of  claim 1 , wherein said uppermost magnetic layer has a residual magnetic flux density {Br(u)} from 2,000 to 7,000 G and said lowermost magnetic layer has a residual magnetic flux density {Br(L)} from 1,000 to 5,000 G. 
     
     
       13. The magnetic recording medium of  claim 1 , wherein said uppermost magnetic layer has a residual magnetic flux density {Br(u)} from 3,000 to 6,000 G and said lowermost magnetic layer has a residual magnetic flux density {Br(L)} from 1,500 to 4,000 G. 
     
     
       14. The magnetic recording medium of  claim 1 , wherein aid nonmagnetic layer has a thickness from 0.5 to 3 μm. 
     
     
       15. The magnetic recording medium of  claim 1 , wherein said nonmagnetic powder is selected from titanium oxide, zinc oxide, iron oxide or barium sulfate. 
     
     
       16. The magnetic recording medium of  claim 1 , wherein a total weight of a nonmagnetic material which is a solid at an ordinary temperature and contained in said uppermost magnetic layer is larger than a total weight of a nonmagnetic material which is a solid at an ordinary temperature and contained in said lowermost magnetic layer.